Earthquake swarm in desert fading away

The swarm of earthquakes that shook San Diego County on Sunday is fading away, though there's a chance that it could come back to life at any time, says the U.S. Geological Survey.

"These swarms tend to last only one, two or three days," says Susan Hough, a seismologist at the USGS in Pasadena. "We're not really sure why. We don't know that much about them."

An area south of the Salton Sea, between the San Andreas and Imperial faults, erupted with quakes early Sunday. By midnight, more than 40 quakes measuring from 3.0 to 5.5 had been recorded. The shaking included a 5.3 event at 11:33 a.m. and a 5.5 at 1:57 p.m. The quakes caused some damage in nearby Brawley.

On Monday, the shaking greatly declined. There were only five quakes measuring 3.0 or higher. The largest event was a 4.2 at 7:01 p.m.

Quake swarms can cause a lot of anxiety, especially when they're on or near the San Andreas. But Hough noted that there hasn't been a single case in the past century when a local swarm led to a large quake.